This study focused on in vivo osteogenic capability of bone marrow mesenchymal stem cells (MSCs) seeded on ceramic scaffold. Human MSCs from a single donor were seeded on hydroxyapatite porous ceramic (HAP) and were induced to the osteogenic lineage during in vitro culture condition, then the MSCs/HAP composites were implanted subcutaneously into immunodeficient rats. The cellular activities of the composites were assayed in order to evaluate the distribution and differentiation capability of seeded MSCs before and after implantation. These results showed that the new bone, after implantation, was derived from the donor MSCs, which adhered to the surface of the ceramics pore areas during in vitro culture. Therefore, the engrafted donor cells proliferated and showed continuous osteogenic differentiation within the recipients. Consequently, our study demonstrates the usefulness of MSCs/HAP composites for clinical applications.